Field of the Invention
The invention is directed to an image processing technique and more particularly, to an image processing apparatus and an image processing method.
Description of Related Art
A false contour is caused by coarse quantization. The coarse quantization in most cases results in insufficient precision in image intensity. As a result, a smooth gradation in the image is converted into a step change. Such strip-like step change is referred to as a false contour. A false contour is an artifact in an image, which usually occurs in a region with the smooth gradation.
Before removing the false contour, false contour detection has to be performed on the image. The false contour features in two characteristics: steepness in spatial dimension and amplitude of the step change in intensity. In the conventional method for detecting the false contour generally, whether a certain pixel belongs to the false contour is determined by using a gradient magnitude. The gradient magnitude (or a mean and a variance of magnitude) of the false contour is low. In many cases, a gradient magnitude of some image details (e.g., weak edges or fine textures) is similar to the gradient magnitude of the false contour, and therefore, the use of the gradient magnitude is insufficient for describing a false contour curve. When some image details are detected as the false contours, the image details will be smoothed. Nevertheless, the convention method for detecting the false contour would lead to the loss of some image details.